In the production of hydrocarbons, a wellbore may be drilled to target a zone of interest in which oil or gas is thought to be located. After the wellbore is drilled, casing may be installed in the wellbore. The casing may provide structural integrity to the wellbore and isolate the wellbore to prevent fluids in portions of the formation from flowing into the wellbore, and to prevent fluids from the wellbore from flowing out into the formation. Casing may be formed of strings of steel or other metallic tubulars that line the wellbore. Cement may be pumped into an annular region around the outer surface of the casing and allowed to cure to secure the casing in place.
Portions of casing may be removed in order to facilitate certain downhole operations such as sidetracking, hydraulic fracturing, slot recovery, and wellbore abandonment. For instance, in sidetracking, a whipstock may be anchored in the wellbore and a milling tool may be tripped into the wellbore. The milling tool may be guided by the whipstock into the casing. By rotating the milling tool and applying weight or another downhole force, the milling tool may cut and mill away a portion of the casing to form an opening or window. The milling tool or a drill bit may then be extended through the window in the casing in order to drill a deviated or other lateral borehole. In a slot recovery or wellbore abandonment operation, a section mill may be inserted into the wellbore. The section mill may include blades that expand outward and contact the casing. As the section mill is rotated and moved longitudinally within the wellbore, a full circumference of a section of casing may be removed from around the wellbore.